In a resistance spot welding process, a pair of electrodes forcibly clamps at least two weld pieces comprised of metal materials together and a current is applied to the weld pieces via the electrode tips. As the current flows, the temperature of the weld pieces increases until the inherent melting point of the weld pieces, at which point the weld pieces are forged together and a weld is formed.
Previously, the processes of spot welding utilized control methods that included constant current, constant voltage, constant heat, and other methods. In the constant voltage and constant current method, the voltage or current are kept constant for the duration of the weld period, thereby resulting in an excess amount of heat being supplied to the weld zone. In the constant heat method, a linear power curve controls the welding process. Constant heat techniques, however, cannot be optimized to produce a high nugget diameter to energy ratio because of the nonlinear and dynamic characteristics of the welding process.
Furthermore, constant heat and a number of other welding systems incorporate a probe wire measuring the voltage at the electrodes to determine the resistance of the weld pieces during the weld process. Probe wires, however, often break, thereby stalling the welding process. As these weld guns are used in industrial applications, a broken probe wire can shut down an entire assembly line, which can result in costly production delays. Thus, there is a need for probeless energy delivery control in spot welding processes.